In the field of toners for electrophotography, with the progress of electrophotographic systems, it has been demanded to develop toners adaptable for high image quality and high printing speed. From the viewpoint of the high image quality, it has been required that colorants used in the toners are in the form of finely divided particles. However, the colorants are hardly dispersed in the toners, thereby causing problems such as deteriorated image density.
In recent years, so-called chemical prepared toners have been used because of a small particle size and a narrow particle size distribution thereof. However, it tends to be difficult to apply a mechanical shear force to the chemical prepared toners when dispersed unlike so-called pulverized toners, so that a pigment fails to be well dispersed therein, which results in difficulty in attaining a high image density.
As to the chemical prepared toners, there are disclosed, for example, the technique using a self-dispersible pigment (Patent Document 1), the toner produced from a pigment dispersion prepared by dispersing a pigment using a surfactant as a dispersant (Patent Document 2), etc. In addition, there is also known the method in which a kneaded material obtained by previously melt-kneading a resin and a colorant is emulsified (Patent Document 3). However, this method tends to be deteriorated in productivity owing to an increased number of production steps, and further the colorant tends to be poor in dispersibility in the resin. Therefore, there is an increasing demand for toners capable of forming images having a sufficient density.
Patent Document 1: JP-A 2005-275145
Patent Document 2: JP-A 2003-316079
Patent Document 3: JP-A 2006-171692